1. Field of the Invention
The present invention relates to a communications earpiece and more particularly to an open ear canal earpiece which is capable of cancelling noise present in an ear canal.
2. State of the Art
In various circumstances ambient noise can interfere with transmission and receipt of sound information. U.S. Pat. No. 4,473,906, which is incorporated herein by reference, discloses an active noise cancellation headset which involves connecting the output of a microphone to the input of a speaker via an inverting operational amplifier. The output of the microphone is connected to the inverting input of the operational amplifier, and the non-inverting input of the operational amplifier is grounded. An area around the microphone constitutes a xe2x80x9cclosed volume.xe2x80x9d The microphone and speaker are placed in close proximity to one another so that the speaker is within the closed volume area around the microphone.
In operation, any ambient noise in the closed volume is sensed by the microphone. This output is amplified and inverted by the operational amplifier, and then used to drive the speaker to create an equal and opposite ambient noise which is then supplied back to the microphone. The microphone includes a diaphragm which is moved in response to the ambient noise. The output from the speaker creates an equal and opposite pressure on the microphone diaphragm which counteracts the ambient noise. In other words, the output of the microphone is servoed by feedback from the speaker to the zero condition at the non-inverting input of the operational amplifier.
The advantage of this circuit is that it is a virtual earth active noise cancellation system which does not require phase or amplitude tuning. Rather, the only requirement is that the speaker be placed within the closed volume of the microphone to establish a uniform pressure throughout the closed volume and a zero output condition from the operational amplifier.
The noise cancellation technology of the ""906 patent can experience some problems when low frequency high intensity sounds are detected by the microphone. The noise cancellation system will attempt to cancel this noise by driving the speaker to create an equal and opposite pressure on the microphone diaphragm. However, because the speaker can not be driven at such levels without distorting, the low frequency high intensity noise is not cancelled. Furthermore, when the speaker is driven to such an extent, the speaker will create audible noise which exacerbates the noise problem.
U.S. Pat. No. 5,452,361, which is also incorporated herein by reference, constitutes an improvement of the basic noise cancellation technology described in the ""906 patent. The ""361 patent addresses this overload condition by removing very low frequencies which are inaudible.
A typical hearing aid system involves either an ear canal device, which completely plugs the ear or the use of a behind-the-ear ear device which connects to an ear mold that completely plugs the ear. In both cases, the entire ear canal is blocked to create a closed volume space within the ear canal. Such a small space can be pressurized using a relatively small speaker driver and speaker, since the volume of air that must be moved by the speaker diaphragm to cancel low frequency sounds is relatively small. Because hearing aid systems typically include closed volume space, the relatively small speakers of a typical hearing aid system can be used to reasonably effectively cancel noise in the ear canal.
Although active noise cancellation has been known, it has been previously considered inappropriate for use in open volume applications, such as an open canal hearing aid system, wherein the volume in which the microphone is located is not a closed space. When any portion of the ear canal is open to the ambient air, a small speaker driver can no longer generate the movement of air necessary to cancel low frequency noise.
Noise cancellation bandwidth is a function of the frequencies of the noise to be canceled, the amplitude of those frequencies and the volume of air within which noise cancellation is to be implemented. The cross-over point where effective noise cancellation can be provided decreases, (that is the frequencies for which noise cancellation can be provided expands to include a lower range of frequencies) as the controlled volume becomes smaller. If the controlled volume is increased by opening the ear canal, the frequencies for which effective noise cancellation can be provided increases. For example, noise having a frequency of 50 Hz, has a half wavelength of approximately 10 feet. As such, an open volume with a diameter of nearly 10 feet must be filled with the required cancellation pressure in order to effectively cancel the noise. In other words, the driver must move air for a distance of 10 feet. This is impractical for a hearing aid speaker, which must be configured small in size.
Because of the foregoing difficulties associated with noise cancellation and open volumes, conventional hearing aid systems limited any use of noise cancellation to closed canal systems. Thus, conventional open canal earpieces do not provide for noise cancellation because the driver and speaker which would be required would far exceed the size and power constraints of a typical earpiece.
According to an exemplary embodiment of the present invention, an open canal communications earpiece with noise cancellation is disclosed. The communications earpiece comprises an ear canal tube sized for positioning in an ear canal of a user so that the ear canal is at least partially open for directly receiving ambient sounds. A microphone port in the ear canal tube is located in the ear canal for detecting sounds in the ear canal. A speaker port in the ear canal tube is located in the ear canal for broadcasting sound signals into the ear canal. A sound processor amplifies the ambient sounds received by the microphone to produce processed analog signals. The sound processor also comprises noise cancellation means for producing an inverse noise signal of noise detected in the ear canal by the microphone. The inverse noise signal is sent to the speaker port so as to be broadcast into the ear canal, thereby substantially canceling the ambient noise in the ear canal.
According to an alternate embodiment, the communications earpiece can be configured to fit entirely in the ear canal of the user so long as the ear canal is partially open for receiving ambient sound.